Well cementing composition having improved flow properties containing a polyamido-sulfonic additive

ABSTRACT

Aqueous hydraulic cement compositions containing polyamido-sulfonic compounds as flow-property-improving and turbulence-inducing additives and their use in cementing wells is disclosed.

BACKGROUND OF THE INVENTION:

1. Field of the Invention

The present invention relates to an aqueous hydraulic cement slurrycomposition especially suitable for use in cementing a well.

More particularly, the present invention concerns polyamido-sulfonicadditives for hydraulic cements used in cementing gas and oil wellswhich improve the flow properties of the cement slurry, especiallyfacilitating high flow rates and turbulent flow of the cement slurrywhen it is being pumped to its desired location during the cementingoperation.

"Polyamido-sulfonic", as used herein, refers to water-soluble polymersof N-sulfohydrocarbon-substituted acrylamides.

As used herein, the terms "improve the flow properties" or"flow-property-improving" are intended to describe the manner in whichthe polyamido-sulfonic additive compositions of the present inventionfacilitate or render more efficient the pumping of cement slurries,particularly the pumping of well cement slurries during primarycementing operations. This action is apparently due primarily to areduction in the frictional drag experienced by the cement slurry whileit is being pumped or moved through a confining passageway, but it isnot intended to limit the described action to such a friction reducingeffect, since other effects may also play a role.

The term "turbulence-inducing" is intended to describe the effect of thepolyamido-sulfonic additive compositions of the present invention inpromoting the departure of a moving cement slurry from laminar flow toturbulent flow. The slurry in such a state of flow no longer moves inlaminae aligned along the confining conduit, but experiences adisorganized flow characterized by eddies and disturbances. Theflow-property-improving and turbulence-inducing additives of the presentinvention reduce the apparent viscosity of a cement slurry, which inturn reduces the flow rate required to cause turbulent flow. Thus, thepromotion of turbulent flow may take place simply as a reduction in theamount of pumping pressure or volume necessary to induce a state ofturbulent flow for a particular cement slurry under specific pumpingconditions, below that which would be required if theturbulence-inducing additive were omitted from the cement slurrycomposition.

Techniques for drilling and completing wells, particularly gas and oilwells, and well-established. Of chief concern here are those wells whichare drilled from the surface of the earth to some subterranean formationcontaining a fluid mineral which it is desired to recover. After thefluid-containing geologic formation is located by investigation, abore-hole is drilled through the overlying layers of the earth's crustto the fluidcontaining geologic formation in order to permit recovery ofthe fluid mineral contained therein. A casing is then secured inposition within the bore-hole to insure permanence of the bore-hole andto prevent entry into the well of a fluid from a formation other thanthe formation which is being tapped. This well casing is usuallycemented in place by pumping a cement slurry downwardly through the wellbore-hole, which is usually accomplished by means of conducting tubingwithin the well casing. The cement slurry flows out of the open lowerend of the casing at the well bottom and then upwardly around the casingin the annular space between the outer wall of the casing and the wallof the well bore-hole. The drilling process which produces the bore-holewill usually leave behind on the wall of the bore-hole produced, adrilling fluid filter cake of mud-like material. This material is abarrier to the formation of proper bonding by any cement compositionemployed to produce an impermeable bond between the casing and the wellwall. As a result, cementing operations have often proven inadequate,permitting fluids from other formations to migrate into the producingformation, and vice versa. Prior art solutions to this problem haveincluded washing away the filter cake from the well wall prior to thecementing operation. However, the washing liquids themselves haveintroduced new problems, including reduced permeability of the producingformation.

Nevertheless, an effective cementing operation requires that thedrilling fluid filter cake be removed from the well bore wall andreplaced by the cement slurry in order to permit the formation of asolid layer of hardened and cured cement between the casing and thegeologic formations through which the well bore-hole passes. It has beenrecognized in the art that removal of the drilling fluid filter cake maybe accomplished by a sufficiently high flow rate for the cement slurryduring its injection into the well bore-hole. Such a high flow rate willusually occur as turbulent flow.

The flow properties of cement slurries are also important during primarycementing operations in other respects. The pressure drop in the annulusbeing cemented which results from friction will increase both thehydraulic horsepower required to move the cement slurry into place in agiven time period, as well as the hydrostatic pressure exerted on theproducing formation. Moreover, some investigators have felt thatobtaining actual turbulent flow of the cement slurry is not necessary toremove the drilling fluid filter cake, and that high flow rates aresufficient where the drilling fluid has low gel strength and there isgood centralization (concentric placement of the well casing within thewell bore-hole). Consequently, the present invention is directed to wellcementing compositions having improved flow properties, including, butnot limited to, adaptability to turbulent, especially high turbulentflow.

Prior to the discovery of flow-property-improving, especiallyturbulence-inducing additives for well cement compositions, achievinghigh flow rate and turbulent flow for conventional cement slurriespresented a number of problems not normally encountered with lessviscous fluids. Inducing turbulence by control of flow rate alone hasrequired a certain minimum velocity, which in turn is dependent uponmaintaining a certain minimum pressure. Particularly, where theturbulence induced is sufficient to assure removal of drilling fluidfilter cake, additional pumping capacity and very high pressure levelsare required. Producing high flow rates has, of course, required thesame measures. These required pressure levels, especially for deepwells, have often exceeded the pressure at which many subterraneanformations break down, thus giving rise to a problem of lostcirculation. It also may happen that the required pressure level exceedsthe capacity of the pumping equipment or the endurance of the welldrilling and associated apparatus.

The present invention facilitates pumping of cement slurries at highflow rates and permits pumping of cement slurries in turbulent flow atsignificantly lower flow rates than would be possible using conventionalcement slurry compositions, by adding to the said cement slurries aflow-property-improving and turbulence-inducing agent. The lower flowrates required for turbulence result in a corresponding reduction in thepump pressures required to force the cement slurry into place in thedesired manner. Correspondingly, higher flow rates may be achieved witha reduced amount of required pressure and pumping capacity.

The present invention also permits increased use of fluid-loss controlagents which have a viscosity-increasing effect on cement slurries withwhich they are employed. This thickening tendency otherwise requires useof only small amounts of fluid-loss control agents to avoid problems inpumping of an overly viscous cement slurry. Use of theflow-property-improving and turbulence-inducing additives of the presentinvention in conjunction with fluid-loss control agents produces acement slurry having desirable flow properties, yet containing adequatequantities of the fluid-loss control agent.

2. Description of the Prior Art

U.S. Pat. No. 3,359,225 discloses an additive for Portland-type cementscomprising polyvinylpyrrolidone and the sodium salt of naphthalenesulfonate condensed with formaldehyde. The additive reduces the frictionencountered as the cement is flowed or pumped into place, and alsopermits the utilization of decreased quantities of water in the cementmixture. Harrison - U.S. Pat. No. 3,409,080 discloses an aqueoushydraulic cement slurry containing an O,O-alkylene-O' ,O' -alkylenepyrophosphate-urea pyrolysis product and a water-soluble,water-dispersible polymeric material. The cement composition hasimproved properties whereby it may be injected in a state of turbulencewithout the expenditure of the amount of additional energy usuallyrequired to attain such a state. Kucera - U.S. Pat. No. 3,465,824discloses an aqueous hydraulic cement slurry containing abisulfite-modified phenol-formaldehyde condensation product which servesas a turbulence-inducer to the slurry while being moved in a confinedpassageway. Hook et al. -- U.S. Pat. No. 3,465,825 discloses an aqueouscement slurry containing a turbulence-inducing agent comprising thelithium salt of the condensation product fo mononaphthalene sulfonicacid and formaldehyde. Scott et al. -- U.S. Pat. 3,511,314 discloses anaqueous hydraulic cement slurry containing a turbulence-inducing,fluid-loss control agent consisting of the reaction product of (1) anamino compound selected from the group consisting ofpolyalkylenepolyamines, polyalkylenimines, and their mixtures, and (2)an acidic compound selected from the group consisting of carboxylicacids, sulfonic acids, polymers having a carboxyl substituent, andpolymers having a sulfonate substituent. Messenger - U.S. Pat. No.3,558,335 discloses cement compositions comprising hydraulic cement inadmixture with a turbulence-inducer and silica or diatomaceous earthparticles. A number of known turbulence-inducers are set out, any ofwhich may be employed in the compositions disclosed.

SUMMARY OF THE INVENTION:

In accordance with the present invention there is provided a wellcementing composition comprising hydraulic cement, water, and from about0.01 to about 5.0% by weight of the cement of a flow-property-improvingand turbulence-inducing additive comprising a polyamido-sulfoniccompound. Preferably, this composition contains from about 0.1 to about2.0% by weight (based on dry weight of cement) of the polyamido-sulfoniccompound additive. The present invention also provides a method ofcementing which employs the cement composition just described.

The polyamido-sulfonic compounds employed as flow-property-improving andturbulence-inducing additives for well cementing compositions in thepresent invention may be represented by the following formula: ##EQU1##

wherein R₁ is hydrogen or methyl; R₂, R₃, R₄, and R₅ are eachindependently selected from the group consisting of hydrogen, phenyl,straight or branched alkyl of from one to twelve carbon atoms, andcycloalkyl of up to six carbon atoms; R₆ is straight or branched alkylof from one to twelve carbon atoms, cycloalkyl of up to six carbonatoms, phenyl, or is absent; A is hydrogen, alkali metal ion, orammonium; and n is an integer of from 2 to about 100, such that theweight average molecular weight of the polyamido-sulfonic compound isfrom about 200 to about 10,000, and preferably from about 200 to about1,500.

A particularly preferred polyamido-sulfonic compound for use in thepresent invention is polymeric 2-acrylamido-2-methylpropane sulfonicacid comprising recurring units of the following formula: ##EQU2##

The polyamido-sulfonic compounds used in the present invention may beprepared by way of a number of conventional polymerization routes, andconsequently any such method giving satisfactory yields of acceptablypure product will be suitable.

The compositions and methods of the present invention may employ anytype of hydraulic cement. Hydraulic cement is defined as any cementwhich will set or cure under the action of water, and is intended toinclude all mixtures of lime, silica and alumina, or of lime andmagnesia, silica, and alumina and iron oxide. Hydraulic cements includehydraulic limes, grappier cements, pozzolan cements, natural cements,and portland cements. Pozzolan cements include slag cements made fromslaked lime and granulated blast furnace slag. Among these hydrauliccements, the portland cements are preferred, chiefly because of theirsuperior strength characteristics. The term portland cement is intendedto include any cement regarded in the cementing art as a portlandcement, usually as defined by standard reference works. The precisecomposition of any one particular portland cement will vary fromanother, but generally portland cements are produced by mixing andgrinding together a calcareous and an argillaceous material, kilnheating the mixture (1350° to 1800°C.) until vitrification begins,pulverizing the clinker thus produced and mixing the same with a smallamount of gypsum. The portland cements may be ground to any desiredparticle size, and grading of portland cements is on the basis of thespecific surface of the cement, which will range between 1200 and 2600square centimeters per gram. Grading is also based on the amount ofcement particles retained on a No. 325 Screen, U.S. Sieve Series. Thus,preferred oil well cements have a specific surface of about 1480 squarecentimeters per gram and about 85% by weight passes through a No. 325Screen.

The hydraulic cement may be employed alone in preparing the cementingcomposition of the present invention, merely being admixed with waterand the flow-property-improving and turbulence-inducing additive, or itmay have additionally incorporated therein any of a number ofconventional cement additives. For example, the cement may include aminor portion, up to about 2.0% by weight of dry cement, of a retardercomposition. Such an additive is preferred for oil well cements, sincecementing operations are conducted under ambient well bottomtemperatures which can exceed about 200°F. Examples of conventionalretarder compositions include carboxymethylhydroxyethyl cellulose,borax, dehydrated borax, calcium lignosulfonate and ferrochromelignosulfonate.

Fluid-loss control agents may be employed, as previosly discussed.Well-known fluid-loss agents include such materials aspolystyrenesulfonate, polyvinylpyrrolidone, polyvinyl alcohol,polyvinylacetate, and carboxymethylhydroxyethyl cellulose.

Weighting components comprising inert materials such as barite andilmenite are often employed. Silica may be employed to retard hightemperature strength retrogression.

Other known additives conventionally employed with cementingcompositions may be employed with the cementing compositions of thisinvention, and in amounts sufficient to produce the intendedmodification of the cementing composition characteristics for which anyadditive was selected. More than one such additive, may of course, beemployed at the same time.

The dry hydraulic cement component of the cementing composition of thepresent invention is admixed with water to form a pumpable, settablecement slurry. The cement sets to form a monolithic solid. The waterwhich is employed to form this cement slurry may be any naturallyoccurring water suitable for preparing cement slurries. Particularly,brines of any concentration of calcium chloride or sodium chloride ortheir mixtures are suitable. Sea water may be employed and is thusconvenient in offshore operations. The water should be employed in anamount which is sufficient to produce a pumpable, settable slurry.Excessive amounts of water may produce a weakened finally set cementwhich is lacking in homogeneity owing to the settling of the aggregateportions thereof. Proper amounts of water for producing a suitablecement slurry are described in technical publications, such as thebulletins of the American Petroleum Institute (API). Increasing watercontent in a cement composition effects a lowering of the plasticviscosity of the cement slurry, which results in the slurry being morereadily pumped in turbulent flow. However, the water content should notbe in excess of the amount which will give 4.0 ml. of supernatant waterfor a 250 ml. sample of cement slurry which has been allowed to standundisturbed in a 250 ml. graduated cylinder for a period of two hours.The type of hydraulic cement composition employed will also, of course,determine the amount of water required. Other factors are significant aswell. For example, where silica is added to the cement composition, andhigh temperatures are encountered in the cementing operation (aboveabout 250°F.), additional amounts of water will be required. Generally,the amount of water necessary to give a settable cement compositionhaving the required characteristics, which contains theflow-property-improving and turbulence-inducing additive of the presentinvention will be in an amount of from about 25 to about 60% by weight,based on the weight of dry hydraulic cement.

Water content may be varied in order to effect a change in the densityof the cement slurry. It is customary practice to employ a cement slurrywhich has a density at least as great as that of the drilling fluid usedin the drilling operation. Thus, densified slurries may be produced bydiminishing the amount of water which would otherwise be employed.

The procedure for preparing the cementing compositions of the presentinvention does not require any particular sequence of steps. Thepolyamidosulfonic flow-property-improving and turbulence-inducingadditives of the present invention may be employed in the water-solubleacid, alkali metal or ammonium salt form, and simply added to the waterwhich is used to produce the final cement slurry composition. When otherconventional additives are employed, they may be incorporate into thefinal cement slurry composition in any known suitable manner.

The influence of the turbulence-inducing additives of the presentinvention on the rheological properties of the total cement slurrycomposition is susceptible to mathematical characterization. Expertopinion varies as to the correct theoretical model, and thus the propermathematical characterization of the rheological properties of cementslurries. They have been treated according to the principles of Binghamplastic fluids as well as according to the Power Law concept. Themathematical formulation is based on Fann Viscometer readings, as willbe described hereinafter.

The behavior of cement slurries may be viewed as governed by the PowerLaw concept. For a mathematical characterization of this concept, twoslurry parameters are determined: the flow behavior index (n') and theconsistency index (K'). A Fann Viscometer may be used to make thesedeterminations. The instrument readings at 600 and 300 r.p.m. arerecorded and the values for n'and K' are then calculated as follows:##EQU3##

where N is the extension factor of the torque spring of the particularFann Viscometer instrument.

The so-called Reynolds Number for a fluid moving through a conduit isthe critical value at which the flowing fluid will begin to flow inturbulence. The Reynolds Number may be calculated according to thefollowing equation: ##EQU4## where: N_(Re) is the Reynolds Number(dimensionless),

V is the velocity, feet per second,

π is the slurry density, pounds per gallon,

n' is the flow behavior index (dimensionless),

K' is the consistency index, pound-seconds per square foot,

D is the inside diameter of the pipe, inches.

The velocity (V_(c)) at which turbulence may begin is readily calculatedfrom the following equation, which is derived from the equation for theReynolds Number, and assumes a Reynolds Number of 2100: ##EQU5##

where the different elements of the equation have the same meaning asindicated above for the Reynolds Number equation. Where the conduitthrough which the cement slurry passes is the annulus between the wellcasing and the well wall, D = D_(O) - D_(I), where D_(O) is the outerinside diameter or hole size in inches, and D_(I) is the inner pipeoutside diameter in inches.

The Power Law concept equation will give higher flow rates, or lowerflow rates required to produce turbulence where the Fann Viscometerreadings are reduced.

EXAMPLE Fann Viscometer Readings for a Cementing Composition ContainingPoly-(2-acrylamido-2-methylpropane-1-sulfonic acid)Flow-Property-Improving and Turbulence-Inducing Additive

A 38% Class H (APl Class H cement has a fineness in the range of1400-1600 sq. cm./gram, and contains, in addition to free lime andalkali, the following compounds in the indicated proportions: tricalciumsilicate - 52, dicalcium silicate - 25, tricalcium aluminate - 5,tetracalcium aluminoferrite - 12, and calcium sulfate - 3.3) cementslurry was made up by adding tap water (228 ml.) to a Waring blender,dissolving the indicated amount ofpoly-(2-acrylamido-2-methylpropane-1-sulfonic acid) turbulence-inducingadditive in the water, then mixing in the cement (600 g.) at low speed.Molecular weight of the poly(2-acrylamido-2-methylpropane-1-sulfonicacid) was estimated to be less than 1000. The resultant slurry was thenmixed at high speed for 35 seconds. The slurry was then stirred at highspeed on a laboratory gang-stirrer for 20 minutes. The viscocity of theslurry was then immediately measured on a Fann Viscometer equipped witha No. 1 spring. The instrument readings for various speeds were recordedand are illustrated in the table of values below.

    __________________________________________________________________________                % Additive                                                                          Fann Viscosities at                                         Turbulence- (based on                                                                           Indicated R.P.M.'s                                          Inducing    weight of                                                         Additive    dry cement                                                                          600   300   200   100                                       __________________________________________________________________________    Control*    --    165   105.5 87.5  65                                        Poly-(2-acrylamido-                                                           2-methylpropane-1-                                                                        0.5   114.5 48.5  34.5  18.5                                      sulfonic acid)                                                                            0.25  104   88.5  53.5  25.5                                      __________________________________________________________________________     *Neat Class H cement.                                                    

The polyamido-sulfonic flow-property-improving and turbulence-inducingadditive of the present invention is employed to prepare cementingcompositions which are readily pumped in turbulent flow during acementing operation at a satisfactorily low pump rate. The additive isalso used to advantage simply to reduce the pumping pressure requiredfor a given flow rate, or to obtain a higher flow rate at a givenpumping pressure. The cementing composition of this invention which hasimproved flow properties and is easily flowed in turbulence is employedin the conventional cementing operation in the same manner as would acementing composition which did not contain the flow-property-improvingand turbulence-inducing additive, but which was otherwise the samecomposition.

Obviously, many modifications and variations of the invention ashereinabove set forth can be made without departing from the essence andscope thereof, and only such limitations should be applied as areindicated in the appended claims.

What we claim is:
 1. A cementing composition comprising hydraulic cementin admixture with from about 0.01 to about 5.0 percent by weight, basedon weight of hydraulic cement, of a polyamido-sulfonic compoundrecurring units represented by the following formula: ##EQU6## whereinR₁ is hydrogen or methyl; R₂, R₃, R₄, and R₅ are each independentlyselected from the group consisting of hydrogen, phenyl, straight orbranched alkyl of from one to twelve carbon atoms, and cycloalkyl of upto six carbon atoms; R₆ is straight or branched alkyl of from one totwelve carbon atoms, cycloalkyl of up to six carbon atoms, phenyl, or isabsent; A is hydrogen, alkali metal ion or ammonium; and n is an integerof from 2 to about 100, such that the weight average molecular weight ofthe polyamido-sulfonic compound is from about 200 to about 10,000. 2.The composition of claim 1 wherein the weight average molecular weightof the polyamido-sulfonic compound is from about 200 to about 1,500. 3.The composition of claim 1 wherein the said polyamido-sulfonic compoundis admixed with the hydraulic cement in an amount of from about 0.1 toabout 2.0 percent by weight, based on weight of hydraulic cement.
 4. Thecomposition of claim 1 wherein the polyamido-sulfonic compound ispoly-(2-acrylamido-2-methylpropane-sulfonic acid) comprising recurringunits of the following formula: ##EQU7##
 5. An aqueous hydraulic cementslurry composition having improved flow properties and being morereadily induced to flow in turbulence, comprising dry hydraulic cementin admixture with from about 0.01 to about 5.0 percent by weight, basedon weight of dry hydraulic cement, of a polyamido-sulfonic compoundhaving recurring units represented by the following formula: ##EQU8##wherein R₁ is hydrogen or methyl; R₂, R₃, R₄, and R₅ are eachindependently selected from the group consisting of hydrogen, phenyl,straight or branched alkyl of from one to twelve carbon atoms, andcycloalkyl of up to six carbon atoms; R₆ is straight or branched alkylof one to twelve carbon atoms, cycloalkyl of up to six carbon atoms,phenyl, or is absent; A is hydrogen, alkali metal ion or ammonium; and nis an integer of from 2 to about 100, such that the weight averagemolecular weight of the polyamido-sulfonic compound is from about 200 toabout 10,000; and sufficient water to make a pumpable slurry which iscapable of setting to form a monolithic solid.
 6. The composition ofclaim 5 wherein the weight average molecular weight of thepolyamido-sulfonic compound is from about 200 to about 1,500.
 7. Thecomposition of claim 5 wherein the said polyamido-sulfonic compound isadmixed with the hydraulic cement in an amount of from about 0.1 toabout 2.0 percent by weight, based on weight of dry hydraulic cement. 8.The composition of claim 5 wherein the water is present in an amount offrom about 25 to about 60 percent by weight, based on weight of dryhydraulic cement.
 9. The composition of claim 5 wherein thepolyamido-sulfonic compound ispoly-(2-acrylamido-2-methylpropane-1-sulfonic acid) comprising recurringunits of the following formula: ##EQU9##